Inner cover for hood-type furnaces



Oct. 25, 1949. H. H. ARMSTRONG I 2,435,995

INNER COVER FOR HOOD-TYPE FURNACES Filed Nov. 22, 1946 3 Sheets-Sheet l HARRY H ARMS rg0/ve BY v /4 TTONEY Oct. 25, 1949. H. H. ARMsTRcNG INNER COVER FOR. HOOD-TYPE FURNACES 3 Sheets-Sheet 2 Filed Nov. 22, 1946 Fiyi INVENTOR.

Oct. 25, 1949. H. H. ARMSTRONG INNER COVER FOR HOOD-TYPE FURNACES v 3 Sheets-Sheet 3 Filed Nov. 22, 1946 G WM mw M R A, Hamm Patented Oct. 25, 1949 INNER COVER FOR HOOD-TYPE FURNACES Harry H. Armstrong, Cleveland, Ohio, assigner, by mesne assignments, to Lee Wilson, Rocky River,

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Application November 22, 1946, Serial No. 711,784

3 Claims. (Cl. 263-43) This invention relates generally to annealing furnaces and, in particular, to an improved inner cover adapted to be used with a hood-type furnace for the annealing of a charge in the form of coils.

This is in part a continuation of my copending application, Serial No. 617,359, filed September 19, 1945, now abandoned.

Hood-type furnaces have come into extensive use for annealing in recent years. Such furnaces represent a marked advance over the earlier practice of heating a charge enclosed in an annealing box in a stationary furnace. A considerable period of time is 'still required, however, to raise the temperature of the charge to the desired point and, even though a single heating hood or furnace is usually placed over a plurality of bases in succession, the production of annealed material in tons per hour is such that the cost of annealing per ton is high. Various expedients have been tried in order to shorten the annealing cycle such as circulation of the atmosphere inside the inner or protective cover and in the case of annealing strip in coils, the use of spacers between the stacked coils forming the charge, to permit absorption of heat through the edges of the coil laps, i, e., axially instead of radially through successive thicknesses or laps.

I have invented an improved inner cover adapted to be used with conventional hood-type furnaces whereby the heating stage of the annealing cycle may be materially shortened so that a single heating hood may cooperate successively with a larger number of bases than has been possible heretofore, thus increasing the output of annealed material. In a preferred embodiment, the inner cover of my invention comprises a side wall and a top, being open at the bottom so it can be disposed over a charge. An inner wall or baille extends around the cover spaced inwardly from the side wall and concentric therewith. The bafe insures intimate contact between the atmosphere within the cover, when cir- -culated by the usual centrifugal fan in the base,

invention will be explained during the following detailed description referring to the accompanying drawings illustrating a preferred embodiment. In the drawings,

Figure 1 is a central vertical section through a hood-type furnace and an inner cover incorporating the invention;

Figure 2 is a portion of Figure 1 to enlarged scale;

Figure 3 is a view similar to Figure 2 showing a modification;

Figure 4 is a vertical central section through a further modification; and

Figure 5 is a portion of Figure 4 to enlarged scale.

Referring now in detail to the drawings, a hood-type furnace of known construction comprises a hood proper shown at IIJ removably disposed on a base II. The hood includes a struc-v tural frame I2 and a refractory lining I3. Heating means of any desired type is mounted in the hood. In the example illustrated, radiant tubes I4 extend vertically within the hood and are heated by the combustion of fuel supplied at their lower ends.

The base I I includes a structural frame I5 and a refractory lining or hearth I I5 with a cover plate I6a thereon. A charge support I1 is carried at a suitable elevation above the hearth on posts I8 pivotally mounted on the structural frame I5 as more fully disclosed and claimed in my copending application, Serial No. 575,680,

filed February 1, 1945, now Patent 2,414,996, isf sued January 28, 1947. The support I'I has a central opening therein. The base is provided with a sealing channel I9 adapted to be penetrated by a sealing flange carried by the hood.

A plurality of coils 20 stacked coaxially on the support I'I form the charge to be annealed. Spacers 2I are disposed between adjacent coils and between the bottom coil and the support. An inner cover 22 is disposed over the charge before the hood IIJ is lowered onto the base. It is to this inner cover that my invention particularly relates. As shown in the drawings, the cover 22 comprises a side wall 23 and a top 24, thus forming an open-bottomed enclosure for the charge. The cover is preferably fabricated from plate of suitable thickness. The lower edge of the j support I1.

cover ts within a sealing channel 25 on the hearth or lining of the base.

The cover 22 has an inner wall or baille 26 extending therearound terminating short of the top andbottom thereof and spaced inwardly of the side wall 22. The baille 26 has a body which is the same shape in section as the inner cover, preferably cylindrical, for the greater portion of its height, but has a frusto-conical bottom ring 21 `welded thereto which tapers downwardly. The baille 26 fits loosely within the cover 22 and is maintained in substantially concentric relation therewith by ribs 28 secured as by welding to the inner surface of the side wall of the cover and spaced circumferentially thereof. This permits the cover and baille to expand and contract independently of veach other. Inwardly sloping ribs 29 are welded to the cover 22 adjacent the lower edge in circumferentially spaced relation and are adapted to engage the frusto-conical rportion 21 of the baille so as to lift it with the cover when the latter is raised as for removal of the charge after completion of the annealing. l The base II is provided with a centrifugal fan 30 mounted centrally thereof below the charge The fan is mounted on a. shaft journaled in suitable bearing brackets 3| and is driven by any convenient means. It will be apparent that the fan when driven forces the atmosphere within the cover outwardly. Circulation of the atmosphere is thus established from below the charge support I1, upwardly through the space between the side Wall of the inner cover and the baille 26 and thence downward- ,f ly inside the latter, through the spaces between coils afforded by the spacers 2I and thence downwardly through the eyes of the coils and the central opening in the support I1 to the fan. A lplate 32 is preferably disposed over the eye of the uppermost coiling stack to insure that the circulating atmosphere passes through the spacers before descending the flue formed by the eyes of the several coils.

By this mode of circulation, the atmosphere is brought repeatedly into intimate contact with the side wall of the inner cover which is subjected to the radiant heat from the tubes I4 and the rate of transfer of heat to the charge is thereby greatly accelerated. Both the inner Icover and the heating hood are manipulated in the Same manner as heretofore, being placed over the charge at the beginning of the heating stage and lifted therefrom, respectively, at the end of the heating stage and the cooling stage. As above pointed out, the baille or inner wall of the cover, although fitting loosely within the latter, is automatically picked up and removed when the cover is lifted. When the inner cover is placed over the charge, the baille or inner wall 26 bottoms on the support I1 just before the inner cover proper bottoms on the hearth or lining of the base.

In order to improve the circulation of atmosphere described above, I employ a frusto-conical ring 33 extending around the base within the inner cover.

In a modified form of my inner cover shown in Figure 3, the baille or inner wall 26 comprises a cylindrical portion 34 and a frusto-conical portion 35 which is separate therefrom but coaxial therewith. The cylindrical portion 34 is welded to spacer ribs 36, thus the lower portion 35 is -the only part of the baille which is lifted by the ribs 29.

In a further modication shown in Figures 4 and 5, the inner cover 22' has a baille 31 spaced inwardly thereof similar to the baille 26. The baille includes a cylindrical body 38 and a frustoconical bottom ring 39 welded'thereto. Centering :pins 40 are welded to the body 38 at spaced points around the exterior thereof. The baille 31 ts loosely within the inner cover but is secured thereto at the bottom, being welded to 'web plates 4I as shown at 42. These plates are welded as at 43 to the interior of the cover. The bottom ring 39 is designed to engage'the charge support I1 before the bottom of the cover 22a engages the hearth. Thus the cover is carried on the charge support by the bottom ring 39 and the bottom o-f the cover is free to expand and contract without restraint. This eliminates distortion of the cover which occurs when the bottom thereof engages the hearth more or less firmly, because of the difference between the coeilcient of expansion of the brick of the hearth and that of the metal of the cover. The coeilicients of expansion of the metal of the charge support land that of the cover are so close together that there is no distortion of the bottom ring 39 which carries the entire weight of the cover and baille. The bottom of the cover thus serves only as a floating sealing skirt. Since the baille is secured to the cover only at the bottom, it is free to expand or contract vertically at a rate different' from that at which the cover expands or contracts.

It will be apparent from the foregoing that the invention is characterized by numerous advantages. In the first place, the inner wall or baille of the inner cover produces a much more efficient heating of the charge by convection than was possible by inner covers known previously, because it insures intimate contact between the atmosphere within the inner cover which is the sole heat-transfer medium, and the side wall of the cover proper to which the heat is supplied. In the second place, the invention involves only a slight increase in the cost of the inner cover and no change in the operating procedure. The improved eiiiciency of heat transfer between the heating elements of the hood and the charge is reflected in a material reduction in the length of the heating stage of the annealing cycle. This permits a single hood to heat successively the charges on ya. larger number of basesrthan was heretofore possible, thus greatly increasing the output of annealed strip and reducing the cost of the annealing operation.

Although I have illustrated and described but a preferred embodiment of the invention, it will be recognized that changes in the construction disclosed may be made without departing from the spirit of the invention or the scope of th appended claims.

I claim:

1. An inner cover for use within a hood-type furnace .comp-rising a side wall, a top wall, -a baille wall spaced inwardly from slaid side wall and terminating short of the top- Eand bottom of said side wall, said baille wall including a frusto-conical lower portion tapering downwardly, and sloping ribs on said side wall adapted to engage said lower portion when said inner cover is raised. y

2. An inner cover for use within a hood-type furnace comprising :a side wall, a top wall, a baille wall spaced inwardly from said side wall and terminating short of the top and bottom of said side Wall, said baille wall including a frustoconical lower portion tapering downwardly, and

sloping ribs on said side wall adapted to engage said lower portion when said inner cover is raised, said lower portion of said baie wall being permanently united with the remainder of the baffle wall.

3. An inner cover for use within la hood-type furnace comprising a side wall, a top, a blame Wall spaced inwardly of said side wall and terminating short of the top and bottom of said side wall, said baie Wall tting loosely within the inner cover, ,and ribs spaced circumferentially of the inner surface of the side Wall for maintaining the baffle Wall generally concentric with the cover.

HARRY H. ARMSTRONG.

6 REFERENCES CITED The following references are of record'in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,622,494 Cranston Mar. 29, 1927 1,794,151 Cope Feb. 24, 1931 1,825,790 Hansen Oct. 6, 1931 1,923,145 Harsch Aug. 22, 1933 1,940,948 Harsch Dec. 26, 1933 2,168,028 Harsch Aug. 1, 1939 2,276,971 Hoak Mar. 17, 1942 2,325,677 Hoak Aug. 3, 1943 

